Mar 23 2017

Enable Google Authenticator 2FA for the SSH on your Raspberry PI

1.Install the lib and the program

@raspberrypi:/# sudo apt-get install libpam-google-authenticator

Reading package lists… Done

Building dependency tree

Reading state information… Done

The following extra packages will be installed:

libqrencode3

The following NEW packages will be installed:

libpam-google-authenticator libqrencode3

0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.

Need to get 59.7 kB of archives.

After this operation, 117 kB of additional disk space will be used.

Do you want to continue? [Y/n] y

Get:1 http://mirrordirector.raspbian.org/raspbian/ jessie/main libqrencode3 armhf 3.4.3-1 [29.1 kB]

Get:2 http://mirrordirector.raspbian.org/raspbian/ jessie/main libpam-google-authenticator armhf 20130529-2 [30.5 kB]

Fetched 59.7 kB in 1s (48.1 kB/s)

Selecting previously unselected package libqrencode3:armhf.

(Reading database … 35014 files and directories currently installed.)

Preparing to unpack …/libqrencode3_3.4.3-1_armhf.deb …

Unpacking libqrencode3:armhf (3.4.3-1) …

Selecting previously unselected package libpam-google-authenticator.

Preparing to unpack …/libpam-google-authenticator_20130529-2_armhf.deb …

Unpacking libpam-google-authenticator (20130529-2) …

Processing triggers for man-db (2.7.0.2-5) …

Setting up libqrencode3:armhf (3.4.3-1) …

Setting up libpam-google-authenticator (20130529-2) …

Processing triggers for libc-bin (2.19-18+deb8u7) …

@raspberrypi:/#

2. Start the Google Authenticator program and set it up

@raspberrypi:/# google-authenticator

Do you want authentication tokens to be time-based (y/n) y

https://www.google.com/chart?chs=200×200

Your new secret key is: DFDFDSFVSDFSDFSDF

Your verification code is 36534654

Your emergency scratch codes are:

93857601

12345678

09876543

34567890

01928374

Do you want me to update your “/root/.google_authenticator” file (y/n) y

Do you want to disallow multiple uses of the same authentication

token? This restricts you to one login about every 30s, but it increases

your chances to notice or even prevent man-in-the-middle attacks (y/n) y

By default, tokens are good for 30 seconds and in order to compensate for

possible time-skew between the client and the server, we allow an extra

token before and after the current time. If you experience problems with poor

time synchronization, you can increase the window from its default

size of 1:30min to about 4min. Do you want to do so (y/n) y

If the computer that you are logging into isn’t hardened against brute-force

login attempts, you can enable rate-limiting for the authentication module.

By default, this limits attackers to no more than 3 login attempts every 30s.

Do you want to enable rate-limiting (y/n) y

3. Activate Google Authenticator to work with the PAM module and SSH

sudo nano /etc/pam.d/sshd

Add the following line:

auth required pam_google_authenticator.so

 

sudo nano /etc/ssh/sshd_config

locate ChallengeResponseAuthentication line which is set by default to “no”, and change it to “yes”

sudo /etc/init.d/ssh restart

Warning: Do not close the existing SSH session, open a new SSH session to test your Google Authenticator 2FA :)

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